Jan 27, 2016 · QString QString::fromUtf16(const ushort * unicode, int size = -1) const ushort* str = read_raw("hello.txt"); // assuming hello.txt is UTF16 encoded, and read_raw() reads bytes from file into memory and returns pointer to the first byte as const ushort* QString qstr = QString::fromUtf16(str);

Hence this is slower than passing a QString, especially if the QString parameter is much used. I would recommend to always pass a const QString&, and if you need maximum speed on the called side, make a QString copy there, and access this local copy to avoid a double-indirection (faster, less generated code).

QString::compare will only return zero if the string passed to it and the string it is called on are equal. Qstring::operator== returns true if the strings are equal otherwise, false. Since compare only returns zero when the strings are equal then (qstrign_variable.compare("text") == 0) == (qstrign_variable == "text")

@Vitali not correct. "The destructor for the QByteArray may be called before the constructor of the STL string" is not correct statement: Quoting the standard: 12.2.3 Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created.

One drawback though: QString::arg() doesn't handle std::string. You will need to call: QString::fromStdString() on your std::string to make it into a QString before passing it to QString::arg(). Try to separate the classes that use QString from the classes that use std::string. Or if you can, switch to QString altogether.

Sep 14, 2014 · Note that QString::number(0) is decidedly not null - it creates a QString with the value "0". You could also initialize the QString with a NULL pointer, but I wouldn't recommend it unless you're passing a pointer regardless of whether it's NULL or not (i.e., it could sometimes point to a C string) since it's unnecessary.

Jul 24, 2015 · QString eliminates this confusion by using UTF-16 encoding on all platforms. If you need to interact with platform-specific code, QString provides helper methods to convert to and from UTF-8, UTF-32, native std types, etc.

Dec 8, 2020 · QString::arg. You can specify the formatting with QString::arg like: %.3f: QString("%1").arg(1.3, 0, 'f', 3): where the second argument is the field-width (minimum width of the resulting string, 0 here), the third is the format of the number, (in this case f means use no scientific notation), and the fourth is the precision (3 number of decimal places).

The idiomatic way to create an empty QString is using its default constructor, i.e. QString(). QString() creates a string for which both isEmpty() and isNull() return true. A QString created using the literal "" is empty (isEmpty() returns true) but not null (isNull() returns false). Both have a size()/length() of 0.

QString::arg() is overloaded, for example arg(int a1, int a2), but there is no arg(int a1, QString a2), so using QTextStream() and operator << is convenient when formatting longer strings with mixed types.